This invention relates to encoding a television signal, and it is also concerned with the transmission of such an encoded signal, and the reception and decoding of such a signal.
Coding of information is required when it is desired to restrict the reception of the information in intelligible form to certain recipients, for example the subscribers to a television service.
I have described in my earlier co-pending application Ser. No. 930,496, a coding arrangement in which the information-bearing portions of alternate groups of lines are inverted. The number of lines in a group (which number may be one) is randomly selected for each field. The accompanying audio information is coded by conversion of the audio signal to digital form. The present invention is an improvement of my earlier coding system.
Encoding apparatus for television signals in which the information-bearing portions of some lines are inverted are shown in U.S. Pat. Nos. 3,801,732, 3,919,462, 4,022,972 and 4,025,948.